This invention relates to implantable stimulators generally and more particularly to implantable nerve stimulators and pacemakers.
It is known that stimulation of the vagus nerve can reduce the sinus rate, as well as prolong the AV conduction time or, if stimulation energies are high enough, induce A-V block. Use of vagal nerve stimulation to treat supraventricular arrhythmias and angina pectoris is disclosed in the article "Vagal Tuning" by Bilgutay et al., Journal of Thoracic and Cardiovascular Surgery, Vol. 56, No. 1, July, 1968, pp. 71-82. It is also known that stimulation of the carotid sinus nerve produces a similar result, as disclosed in the article "Carotid Sinus Nerve Stimulation in the Treatment of Angina Pectoris and Supraventricular Tachycardia" by Braunwald et al., published in California Medicine, Vol. 112, pp. 41-50, March, 1970.
The nervous system regulating the rhythm of the heart also includes a number of highly ganglionated plexi or "fat pads" at various locations on the heart, including fat pads associated with the SA and AV nodes. The fat pad associated with the SA node is located overlying the right pulmonary vein entrance in dogs, and is located along the anterior AV groove in most humans. The fat pad associated with the AV node is located at the junction of the inferior vena cava and the inferior left atrium in dogs, and is located along the posterior AV groove in most humans.
As set forth in "Functional Anatomy of the Cardiac Efferent Innerration" by Randall et al, in Neurocardiology, edited by Kulbertus etal, Futura Publishing Co., 1988, direct surgical excision of the fat pad associated with the SA node affects the functioning of the SA node without significantly affecting the AV node. Similarly, excision of the fat pad associated with the AV node affects functioning of the AV node without significantly affecting the SA node.
As set forth in the article "Parasympathetic Postganglionic Pathways to the Sinoatrial Node", Bluemel et al, Am. J. Physiol. 259, (Heart Circ. Physiol. 28) H1504-H1510, 1990, stimulation of the fat pad associated with the SA node results in slowing of the sinus rate without the accompanying prolongation of A-V conduction time which normally results from vagal nerve stimulation. The article also indicates that stimulation of the fat pad associated with the AV node is believed to produce corresponding effects limited to the AV node, i.e. extension of the A-V conduction time without concurrent slowing of the sinus rate.
As set forth in the article "Neural Effects on Sinus Rate and Atrial Ventricular Conduction Produced by Electrical Stimulation From a Transvenous Electrode Catheter in the Canine Right Pulmonary Artery" by Cooper et al., published in Circulation Research, Vol. 46, No. 1, January, 1980, pp. 48-57, the fat pads associated with both the AV node and the SA node may be stimulated by means of electrodes located in the right pulmonary artery. The results obtained include both a depression of the sinus rate and a prolongation of the A-V conduction time in response to continuous stimulation at 2-80 Hz at up to 50 ma.